Facsimile telegraph system



Sept. 28,-1937. AA DT 2,094,052

FACSIMILE TELEGRAPH SYSTEM Filed May 22, 1935 2 Sheets-Sheet l lNVE'NTOR8y TAAMODT A TTOR/VEV T. AAMODT FAOSIMILE TELEGRAPH SYSTEM Sept. 28,1937.

Filed May 22, 1935 2 Sheets-Sheet 2 lNl/ENTOR By 7'.AAM007' A TfORNEYPatented 28, 1937 PATENT OFFICE 2. FACSIIIILI TELEGRAPH SYSTEM ThoralfAalnodt, West Brighton, N. Y alllgnor elephone Laboratories,Incorporated,

- New York, N. Y., a corporation of New York Application May 22.1935;Serial No. cases 11 Claims. (Cl. 178-19) This invention relates tosystems for the transmission of intelligence over wires and particularlyto a telegraph system in which the movements of a stylus or writingpoint at a transmitting station are recorded in facsimile at a distantreceiving station.

The object of the invention is a telegraph systern of this type which isvery sensitive in operation and whichvis not affected by variation inthe strength of the line current.

According to the invention the movements of a writing point atthetransmitting station are resolved into two component motions which varythe frequencies of two signal currents being transmitted over the lineand these currents of varying frequency are utilized to producecorresponding movements of the writing point at the receiving station.The two signal frequencies are preferably cutin separate concentricgrooves of the same phonograph record and the variations in thesefrequencies corresponding to the movements of the transmitting writingpoint are obtained by moving reproducers along the grooves to increaseor decrease the relative speed of the record with respect to thereproducer stylus.

At the receiving station the line frequencies are separated and each ismodulated with a local frequency which may be obtained from arecordsimilar to the one at the transmitting station. The frequenciesgenerated at the receiving station each differ normally from thecorresponding line frequency by a predetermined frequency for which thereceiving circuit is balanced in such a way that no motion of thereceiving writing point is produced but any slight change inthe linefrequency due to the motion of the transmitting point unbalances thereceiving circuit and moves the receiving point and the associatedreproducers until the balanced condition is restored. By setting up thereceiving circuit for a balance when the difference between the linefrequencies and the locally generated frequencies is small as com paredwith the line frequencies, the changes in line frequency correspondingto even slight movements of the transmitting point will produce largeunbalancing effects in the receiving circuit and the receiving pointwill follow the movements of the sending point with great accuracy.

An important feature of the invention is a dual 00 direction clutchunitassociated with each reproducer and connected by linkages 'to thewriting point for moving the reproducer back and forth in the groove toproduce the necessary variations in the frequency of the reproduceroutput. 55 Another feature of the invention is a tuned rectifier foreach clutch unit in the receiving circuit which, when unbalanced ineither direction, se-

lectively operates the clutch unit to produce the corresponding motionof the receiving point and the associated reproducer.

By providing both sending and receiving apparatus and the necessaryswitching facilities at each station connected to the line, any stationmay receive matter transmitted from any other station and may transmitto any or all of the 10 other stations. Since the system of thisinvention operates on variations in the frequency rather than variationsin the amplitude of the line current, it is unail'ected by changes inthe line impedance and many receiving stations at diiferent l5 distancesfrom the transmitting station may be operated simultaneously in asatisfactory manner.

In the drawings:

Fig. 1 is a circuit diagram of a facsimile telegraph system according tothe invention; 20

Fig. 2 is a view partly in sectionof one of the dual direction clutchunits;

Fig. 3 is a plan view of the clutch unit; and

Fig. 4 is a perspective view of one of the transmitting and receivingunits shown schematically 25 in Fig. 1.

In the diagram of Fig. 1 the system shown to illustrate the inventioncomprises only two stations H and i2, either one of which may send to orreceive from the other over the line I3, but 30 other similar stationsmay be connected to the line as required.

Each station is equipped with a transmitting and receiving unit I l asshown in detail in Fig. 4,

a transmitting amplifier 15, two tuned rectifiers 5 l6, l1, one for eachcoordinate of motion of the writing point, modulators I8, I! formodulating the line frequencies with those generated locally by thereproducers 2i and 2| in the transmitting and receiving units, thenecessary filters for 40 eliminating undesired frequencies, andswitching facilities for conditioning the station for transmitting orreceiving as desired.

The dual'direction clutch unit of Figs. 2 and 3 consists essentially ofa worm 22 and two worm wheels I! and M concentric with the shaft 25which carries a magnetic disc or diaphragm 26. The worm has both leftand right-hand threads as shown but the worm wheels are cut with leftand right-hand threads respectively so that they are driven in oppositedirections by the worm. The wheels are both normally free to turn withrespect to the shaft II but each is provided with a winding 21, I8which'when energized in a manner to be described attracts the ring 51 onthe 56 diaphragm 25 which is keyed to the shaft 25 and rotates the shaftin the direction in which the corresponding wheel is turning.

The leads for each magnetizing winding are brought to slip rings 10, Hon an'insulating block l2 mounted on the sleeve 13 which turns with theassociated worm wheel. Brush contacts I4, '75 are provided for each pairof slip rings and these contacts are connected with the output circuitof the corresponding rectifier unit IE or ll.

The transmitting and receiving unit of Fig. 4 comprises two clutch units29, 3d of the type just described, a motor 3| for driving the worms ofthese units, and writing and frequency generating mechanism associatedwith the shafts 25 of the units. The writing point '32 is positionedabove the writing pad 33 by linkages 34, 35of the usual type connectedto the shafts 25 of the clutch units. The turntable 36 is driven in anyconvenient manner as by a belt 31 driven from the motor 3| and carries arecord 38 having two pairs of concentric reentrant grooves 39, 40 and50, 5| in whichsuitable single frequencies are recorded. The reproducers20, 2| are adjustably mounted on arms 4|, 42 in such a way that-they maybe quickly and accurately brought into engagement with either groove.For example, the

reproducer supporting structure may be fitted with a spring 69 whichengages slots 10, 10 located in the reproducer arms in the properpositions to lock thereproducer above either selected groove. The armsare pivoted on' the spindle 43 of the turntable 'and connected by cranks44, 45' to the shafts 25 of the clutch units 29 and 30 respectively. Thecranks are fitted with pins 46, 4.1 which slide in slots 48, 49' in thereproducer arms 4| and so that when either shaft 25 is rotated either bythe motion of the writing point in transmitting or by the action of oneof the clutches in the clutch unit itself when the station is receiving,the corresponding reproducer will be moved longitudinally in its groove.During such movement the frequency of the reproduceroutput will behigher or lower than the frequency recorded in the groove depending uponthe direction of the reproducer movement.

One pair of grooves on each record is used for "transmitting and theother pair for receiving.

The signal frequencies are preferably below the range necessary forsatisfactory speech transmission so that the system may function overtelephone lines which are being used for the transmission of telephonemessages. For example, grooves 33 and (iii may be cut at and 200 cyclesper second respectively and grooves 55 and 5i at 90 and cycles persecond respectively.

Assume now that writing or other matter is to be transmitted fromstation ll to station 82. Since all stations would normally beconditioned for receiving it is first necessary to condition station E ifor transmission. moving the reproducers 2d and 25 into engagement withthe grooves 39 and as as shown, closing the switch 52 to connect thereproducers to the amplifier 95, closing switch 53 to connect theamplifier to the line it and starting the driving motor 3i to drive theturntable and the worm wheels of the clutch units 29 and 33.

At station l2 switches 55 and 55 are closed to connect the line and thephonograph reproducers to the tuned rectifiers is, E7, the driving motoris running and the reproducers are engaging grooves 50 and El of the$800 11 33! Under That is done by modulator I8 is being supplied with a90 cycle current from the local reproducer 20 and the modulator IS witha 180 cycle current from the local reproducer 2|.

The filters 59 and 60 select the 10 cycle and 20 cycle differencefrequencies in the modulator outputs and transmit them to the rectifiersI6 and I1 respectively; The rectifiers each comprise two vacuum tubesGI, 62 with their input circuits in push-pull and their output circuitsconnected to the two magnetizingwindings 2'! and 28 of one of the clutchunits already described. Grid leak resistors 63 and 64 are connectedacross the tube inputs, resistor 63 being shunted by an inductance 65and resistor 64 by a capacitance 66 and a small resistor 51 to balancethe resistance of the inductance '55. The values of the inductanc 65 andthe capacitance '55 are such that the rectifier input is tuned to thenormal difference frequency,.in this case 10 cycles per secondforrectifier I6 and 20 cycles per second for the rectifier II. whencurrent is supplied to the rectifier unit at its resonant frequency, thevoltages across the tube input circuits. will be equal so that equalcurrents flow in the two windings of the clutch unit and no clutchingaction takes place. It will be understood that in practice severalstages of amplification may be required for the rectifier units and'thatrectifying devices of other types such as copper oxide 'cycle currentincreases in frequency to 101 cycles,

the input to the rectifier it. at station i2 is then 11 cycles whichconstitutes a ten per cent change fora one per cent change in linefrequency and makes the system inherently of high sensitivity. Underthis condition the impedance of the inductance E5 is greater than normaland the impedance of the capacitance tit is correspondingly less thannormal. Therefore, the electromotive force impressed upon the inputcircuit of tube Si is greater than the electromotive force impressedacross the input circuit of tube 52 and the rectifled current flowing inthe output circuit of tube 6? through the lower winding of clutch unit29 is greater than the current flowing in the output circuit of tube 62through the upper winding of clutch unit 29. The fiux set up in the diaphragm it due to the current in the lower wind-- ing of clutch magnet 25rotates the diaphragm and the shaft 25 with the worm wheel 23 in aclockwise direction so that the reproducer 20 is moved against therotation of the turntableto increase the frequency of the reproduceroutput.

When this frequency becomes 91 cycles the input station I I moves,

'rectifiers may be used to supply power to the plate current in thetubes I and II falls to zero or a low value to cause the clutch torelease the diaphragm and the shaft 25 to stop. Since the writing point32 at the receiving station is connected to the shafts 26 of its clutchunits in the same manner as in the transmitting mechanism the point 32will trace a line similar to the one traced by the transmitting point inchanging the transmitted frequency from 100 to 101 cycles per second.

When the motion of the transmitting point is such that the linefrequency becomes 99 cycles, the receiving mechanism is operated in asimilar manner except that in this case the rectifier input is now of 9cycle frequency so that the electromotive force across the input of tube62 is increased and currentflows to the upper clutch winding 28 and theshaft 25 is rotated contraclockwise by the worm wheel 23. The point 32at station I2 is therefore moved in the opposite direction in accordancewith the motion of the transmitting point and the reproducer 20 is movedwith the rotation of the record until the frequency of its output isreduced from to 89 cycles per seci end at which time the rectifier isagain balanced and the clutch disengaged.

In most cases the motionof the transmitting point wiZi be such as tovary both line frequencies so that rectifier i! at station i2 is niceunbalanced and operates-one or the other of clutches of the unit 351 toreproduce the other coordinate of the motion of the transmittingpointand to move the reproduce!" 2i along its groove and change the f eouencyof its output until the rectifier i'i ifiagain in baiauce. Since thisoperation is identical with that already described for the unit 29 is soved unnecessary to describe in detaii. could be noted however that thesensitivity oi the system is the same for both coordinates c since thelIlOtiOl'l of the transmitting point which changes the cycles current to101 cycles per second if in the proper direction would change the 200cycle current to 202 cycles per second and this modulated with cyclecurrent at the receiving station gives a 22 cycle difl'erence frequencywhich also represents a ten per cent change.

When transmission from station H has been completed the apparatus isreset for receiving by moving the reproducers 20 and 2! at that stationinto contact with the grooves I50 and SI to generate frequencies of 90and 180 cycles per second respectively, and the switches 52 and 53 areclosed in their other positions so that incoming line signals and thelocal frequencies are conducted to the modulators. Then any otherstation, such as II can transmit to station II and the operation of thesystem under these conditions will be clearly understood from theforegoing description.

For purposes of illustration certain definite frequencies have beenmentioned but it will be understood that' these may be modified to suitthe requirements of a particular case and that variousothermodiflcations may be made within the scope of the following claims.

What is claimed is:

1. In a facsimile telegraph system the combination with a writing point,a plurality of moving single frequency recordings, a transmitting lineand a plurality of reproducers for the recordings connected to the line,of means for moving each of the reproducers along its recording inaccordance with .a coordinate of motion of the writing point to vary thefrequencies of the .reproducer 2. In a facsimile telegraph system thecombi- V nation with a transmitting station, areceiving station. a lineconnecting the stations, a movable member at the transmitting stationand means for feeding into the line a plurality of currents each varyingin frequency according to the velocity of the member along onecoordinate of its motion, of a second-movable member at the receivingstation, means for generating a plurality of local currents each varyingin frequency according to the velocity of said second member along onecoordinate of its motion, means for intermodulating each line currentwith one of the local currents and means responsive to the output ofeach of the modulating means for moving the second member along onecoordinate of its motion.

3. In a facsimile telegraph system, the combination with a line, awriting point, two rotatable shafts, linkages between each shaft and thewriting point and means associated with each shaft for generating analternating current, of a pair of oppositely rotating members for eachshaft and means, controlled in accordance with a characten istic of thecurrent from the line and of one of the alternating currents, foroperativeiy associating the shaft with one or the other of said members.

4. In a facsimile telegraph system, a writing point, tine carrying acurrent varying in i"recuency according to the velocity or the pointalong one coordinate of its motion, a second writooint, driving meansfor moving the second point and a source of current varying in.frequency according to the motion of the second point, a moduiator forintermodulating the currents, a rectifier connected to the output of themoduiator for controliing the driving means, and a circuit in therectifier tuned to a frequency equal to the normal difference in thefrequencies of the currents.

5. A facsimile telegraph system according to claim 2, in which thecurrents of variable frequency are generated by reproducers secured tothe movable members and moving iongitudinaily in operative relation tomoving single frequency recordings.

accordance with the motion of the stylus in one of two coordinates.

7. In a variable frequency facsimile telegraph system, the combinationwith a transmitting stylus, linkages for resolving the motion of thestylus into two components, a transmitting line, a disc record havingaplurality of concentric recordings of different frequencies and tworeproducers connected to the line and engaging different grooves of therecord, of reproducer supporting arms pivoted concentrically with therecord, and means for rotating each of the arms in accordance with themotion of one of the stylus linkages.

8. In a facsimile telegraph system, a line carrying two signal currentseach varying in frequency i and receiving mechanism connected to theline local current normally difiering in frequency from one of the linecurrents and varying in frequncy with the angular velocity of the shaft,a circuit tuned to the normal difierence between the frequencies of thelocal and said one of the linecurrents, and means controlled by thecircuit and responsive to changes in the frequency of the line currentfor operatively associating the shaft with one or the other of therotating members.

9: In a facsimile telegraph system, a transmitting station, a receivingstation, a line connecting the stations, a transmitting stylus, meansfor impressing on the line two currents each varying in frequency inaccordance with the velocity of motion of the transmitting stylus in oneof two coordinates, a receiving stylus, two shafts for imparting motionto the receiving stylus in two coordinates, means associated with eachshaft for generating a local current varying in frequency with the speedof rotation of the shaft and means for each shaft operative when thedifference in the frequency between the local current and one of theline currents difiers from a predetermined normal value for selectivelyrotating the shaft move the receiving stylus and Vary the localfrequency to restore the difference frequency to reproducer and saidrecording, of means for changing said relative motion between thereproducer and the recording in accordance with a coordinate of motionof the writing point to vary the frequency of the reproducer output.

ll. In a facsimile telegraph system, a writing point, means including arotatable shaft for moving said writing point along a coordinate of mo--tion, a pair of oppositely rotating members, a source of signalingcurrent, and means for causing said shaft to'he operatively associatedwith one or the other of said oppositely rotating members in accordancewith a characteristic of said signaling current.

THORAIE AAMODI'.

